1. Field of the Invention
The present invention relates to a tape circuit substrate, a semiconductor chip package including the same, and a liquid crystal display (LCD) device including the semiconductor chip package. More particularly, the present invention relates to a tape circuit substrate capable of improving contact reliability and reducing contact resistance between an outer lead of the tape circuit substrate and a pad electrode of an LCD device, a semiconductor chip package including the tape circuit substrate, and an LCD device including the semiconductor chip package.
2. Description of the Related Art
There is currently a trend toward production of large sized image display devices, such as television (TV) monitors, to replace cathode ray tube (CRT) devices. Examples of the image display devices include flat panel display devices such as LCD devices, plasma display panel (PDP) devices, and organic electroluminescent displays (OELD) devices. Of the flat panel display devices listed above, LCD devices that can be made light and thin have been particularly popular.
LCD devices include an upper transparent insulating substrate, on which a common electrode, a color filter, a black matrix, etc. are formed, and a lower transparent insulating substrate, on which a thin film transistor (TFT), a pixel electrode, etc. are formed. A liquid crystal material having an anisotropic dielectric constant is injected between the upper and lower transparent insulating substrates. Different potentials are then applied to the pixel electrode and the common electrode, respectively, to adjust a strength of an electric field formed in the liquid crystal material, thereby changing a molecular alignment of the liquid crystal material. By changing the molecular alignment of the liquid crystal material, light transmitted through the upper and lower transparent insulating substrates is adjusted so that images are displayed. Among such LCD devices, a TFT LCD device using a TFT as a switching element is often used.
An LCD device needs drive-use semiconductor chips to drive a TFT. For a printed circuit board on which drive-use semiconductor chips are installed, a tape circuit substrate made by forming a circuit pattern on a flexible base film is usually used. Connection between a pad electrode of an LCD device and an outer lead of the tape circuit substrate will be described with reference to FIGS. 1A and 1B. FIG. 1A is a plan view illustrating a conventional connection between a pad electrode of an LCD device and an outer lead of a tape circuit substrate. FIG. 1B is a sectional view taken along line B-B′ shown in FIG. 1A.
The tape circuit substrate includes an inner lead (not shown) connected with a bump electrode (not shown) on a drive-use semiconductor chip and an outer lead 12 which is formed on a base film 11 and connected with a pad electrode 22 of an LCD device 21, to which a driving signal for driving a TFT or a power supply voltage signal is input. The pad electrode 22 may include both a first conductive layer 22_2 and a second conductive layer 22_1. The pad electrode 22 of the LCD device 21 contacts the outer lead 12 of the tape circuit substrate in a predetermined region, as shown by the overlap portion of the pad electrode 22 and the outer lead 12 in FIG. 1A.
A method of connecting the pad electrode 22 and the outer lead 12 employs an anisotropic conductive film (ACF) 30, as shown in FIG. 1B. The ACF 30 includes conductive balls 32 dispersed within a thermosetting resin such as an epoxy resin 31. When the ACF 30 is positioned between the pad electrode 22 of the LCD device 21 and the outer lead 12 of the tape circuit substrate and then pressurized, the epoxy resin 31 of the ACF 30 spreads out to a side space of the pad electrode 22 and the outer lead 12. Thus, the epoxy resin 31 is hardened and the conductive balls 32 are pressed between the pad electrode 22 of the LCD device 21 and the outer lead 12 of the tape circuit substrate. As a result, the pad electrode 22 of the LCD device 21 and the outer lead 12 of the tape circuit substrate are electrically connected with each other via the conductive balls 32.
A width W1 of the pad electrode 22 of the LCD device 21 receiving a power supply voltage signal and a width W2 of the outer lead 12 of the tape circuit substrate connected with the pad electrode 22 are greater than a width of other leads and electrodes (for example, a pad electrode of the LCD device 21 receiving a data signal and an outer lead of the tape circuit substrate connected thereto), and therefore, contact resistance between the pad electrode 22 of the LCD device 21 and the outer lead 12 of the tape circuit substrate is reduced. As a result, current flow in the pad electrode 22 of the LCD device 21 and the outer lead 12 of the tape circuit substrate may be increased.
However, when the ACF 30 is positioned and pressurized between the pad electrode 22 having the width W1 and the outer lead 12 having the width W2 for electrical connection, the epoxy resin 31 of the ACF 30 may be hardened without spreading out to the side space. If the epoxy resin hardens without spreading out to the side space, the conductive balls 32 do not satisfactorily contact the pad electrode 22 of the LCD device 21 and the outer lead 12 of the tape circuit substrate.
As a result, contact reliability between the pad electrode 22 of the LCD device 21 and the outer lead 12 of the tape circuit substrate cannot be effectively achieved. Thus, if the width W1 of the pad electrode 22 of the LCD device 21 and the width W2 of the outer lead 12 of the tape circuit substrate are decreased to achieve contact reliability, the contact resistance between the pad electrode 22 of the LCD device 21 and the outer lead 12 of the tape circuit substrate cannot be reduced effectively.